Restricting LSP flooding over IS-IS interfaces

The IS-IS protocol can restrict flooding of LSAs to control sharing of routes between multiple level 2 metro ring networks. You can segregate both level 1 and level 2 networks into flood groups by using area IDs as tags to identify a flood group. Configure interfaces with specific area IDs to modify the flooding behavior as per your requirements. For example, when a router is connected to 5 level 2 metro ring networks, by default all the routers in the 5 rings are flooded with all LSP routes. You can configure 5 distinct flood groups on the ring-facing interfaces on the pre-aggregation device to restrict LSP flooding to a specific area. Configure area IDs on interfaces to segregate them into flood groups. LSPs that belong to the specified area only are flooded through these interfaces. However, self-originated LSPs are not affected by this configuration.